Collagen is an important protein that contributes 30% of all proteins in a living body and functions as a support for bone and cell adherence. For example, collagen is a main constituent element of tissues, such as bone, cartilage, ligament, tendon, corneal stroma, skin, liver, muscle, and the like of the human body. Thus, the collagen material is useful as biomaterials, such as a cell culture substrate, a scaffold material for regenerative medicine (material for tissue engineering of cartilage, bone, ligament, corneal stroma, skin, or liver, for example), an implantation material (wound dressing material, bone grafting material, hemostatic material, or anti-adhesive material, for example) or a carrier for drug delivery. In particular, the collagen material is absolutely imperative for huge tissue regeneration by regenerative medicine. However, a mechanical characteristic of collagen material is not satisfactory and thus, a clinical use thereof is limited.
Hitherto, the following materials are reported as materials obtained by a fibril formation from soluble collagen in vitro. For example, Patent Reference 1 discloses a collagen membrane obtained by forming collagen fibrils from fishskin-derived collagen, freeze drying the obtained collagen gel containing the collagen fiber, and then cross-linking the freeze-dried gel with thermal cross-linking or chemical cross-linking (using a solution of carbodiimide, glutaraldehyde, succinimide or the like). Further, Patent Reference 2 discloses a stretchable collagen material obtained in a solution by forming collagen fibrils from fishskin-derived collagen and chemically cross-linking collagen fibers with a cross-linker, simultaneously.
However, the above materials are porous, and thus, do not have sufficient strength (mechanical characteristic) even after the collagen is cross-linked.
Non-Patent Reference 1 and Non-Patent Reference 2 disclose that a collagen-thin membrane containing collagen fiber is obtained by using a bovine-derived collagen. The collagen-thin membrane has a certain level of strength due to vitrification (drying for at least two weeks), although the collagen-thin membrane is not cross-linked. However, the strength of the collagen-thin membrane is not still sufficient. Therefore, the collagen-thin membrane, wherein the outer edge thereof is reinforced by nylon frame, is only commercially available as a cell culture substrate (Non-Patent Reference 1 and Non-Patent Reference 2).